UNITED NATIONS - Veteran Algerian diplomat Lakhdar Brahimi has agreed to replace Kofi Annan as the international mediator on Syria, UN sources said on Thursday, as the 17-month-old conflict slips deeper into full-scale civil war.

Annan is stepping down at the end of August after six months in the job because he said his Syria peace plan was hampered by a divided and deadlocked UN Security Council.

Diplomats told Reuters on condition of anonymity that Brahimi, who had been undecided for days about whether to accept the offer of the post from UN Secretary-General Ban Ki-moon, did not want to be seen as a mere replacement of Annan but wanted an altered title and mandate. It was not clear when the official announcement would be made, envoys said.